The alternative is an application like F-Secure’s Online Scanner which can be started from a web browser. This particular application is a Java app which means that the latest Java Runtime Environment (JRE) needs to be installed on the system.

Users can visit the official website to start a scan of their computer system right away. The online application uses up to date virus and threat definitions that F-Secure maintains for all of their products.

When you start the online app you are asked to select a scan mode. Available for selection are quick scan, which only scans the most important files and folders of the system, a full scan or a custom scan. Custom scan can be configured on an extra screen in the program interface.

Here it is then possible to scan all or only selected folders and file types. The program itself will scan for malware, spyware, rootkits using a database of known virus signatures and heuristics to identify unknown threats.

The program then downloads files from the Internet which may take some time depending on the Internet connection. The scan time depends largely on the selected mode and the speed of the system.

The application displays a summary after the scan highlighting potentially malicious files. These files can be deleted from the system and send to F-Secure as a sample (handy if heuristics identified an unknown threat that F-Secure has no information about).

The program is easy to use and comes with enough customizations for advanced uses. I would not recommend relying solely on online scanners for security though, but would recommend them for additional security scans on a regular basis. You can check out our overview of online virus scanners here.

The chance is however relatively high that some programs are not updated at all or not early enough which might make the computer system vulnerable to attacks that target vulnerabilities in outdated versions of the programs.

Secunia Online Software Inspector is a cross-browser online scanner for the Windows operating system that can perform a quick scan of the computer system. It is a lightweight version of the security vulnerability checker Secunia Software Inspector that is offered by the same developer.

The only prerequisite is that Java is installed on the PC that the user wants to scan. A click on the Start button will perform a quick system scan. The vulnerability scanner will update the statistics during the scan displaying the total number of programs discovered. This figure is broken down into vulnerable and up to date programs.

It is possible to perform a deeper scan of the PC by checking the Enable thorough system inspection option before starting the scan. Vulnerable applications will be listed by the vulnerability scanner making it very easy to identify programs that need updating. Windows users who want more control over the scanning options can download the desktop software of the client instead. (via Techie Buzz)

An Internet connection is needed on the other hand to perform the scan which sometimes can be a problem if the system is not booting into the operating system. A Live CD could help but many Online Virus Scanners demand the Internet Explorer which is obviously unavailable on Linux systems.

Online Virus Scanners can be used to get a “second opinion” without having to install another anti-virus software on the computer. It is probably a good idea to use as many of the virus scanners as possible if it is suspected that the system was infected by a virus. Below is a list of services that provide access to online virus scanners.

Bitdefender Online Scanner – requires Internet Explorer 4+

Eset Online Scanner – requires Internet Explorer

F-Secure Online Scanner – works only with Internet Explorer 6+

Kaspersky Free Virus Scan – browser independent, downloads roughly 25 Megabytes of files prior to scanning. User can select locations to scan. The scanner does not remove infected files.

McAfee FreeScan – requires Microsoft Internet Explorer 5.5+

Microsoft OneCare Live – requires Internet Explorer.

Panda ActiveScan – requires Internet Explorer or Firefox, does not run in Opera.

Shields Up! – browser independent but very slow and unresponsive currently.

Symantec Security Check – down or gone.

Trendsecure HouseCall – Java based scanner, works with Java compatible browsers.

Windows Security – Trojan scan that requires Internet Explorer 5+

File Scanners:

Avast Online Scanner – file size limit of 512 Kilobyte

Virus Scan – file size limit of 10 Megabyte.

Virus Total – email upload option, 10 Megabyte file size limit.

Do you know any other services where users can scan files or the computer ?

The guys from Virus Total have created a file uploader that makes the whole process comfortable. The 80 Kilobyte application installs itself in the right-click context menu as a Send To entry which in effect means that you can right-click a file on your computer and select Send To > Virus Total to send it to their website to scan the file.

A browser window will open displaying the scan results in the end. This is way more comfortable than to open the Virus Total website and browse for the file on your hard drive once you are there.

The file size limitation of ten Megabytes is still in place however. Another option that you might want to explore is to send them files by email [scan@virustotal.com]. A report is send to the email address that you have used to send the file.